Part cooling fan duct (again!)

DocTrucker

Hall of frame & shame!

There have been a few others others too. Top two have only seen service on my cantilever machines and the two at the bottom right only on the P3Steels. There have been about three iterations of the one looking like a stick man (when fan on top) and the iteration in print of the bottom right is about number 5! I've got to learn my way around OpenFOAM!

Best duct so far has been the bottom left. Currently printing on a modification of the bottom right.

My Notes:

Hot end cannot warm up to temp from cold with fan on 100% (12VDC radial) without faulting out when close to the bed.
Fans hate restriction. Axial far more than radial, but the latter still suffers. The horn like duct was crap!
Bring the ducting to close to the heater block. The closest bit of my vents are about 8mm from the block.
Take care to ensure the power leads for the hotend aren't resting on the duct. They run hot, will soften the plastic and can close vents!
PLA is stiff, PETG is better with temp. Until I get a machine setup to run filled materials the best solution appears to be a mix of both. I've not ran ABS or ASA so haven't got to the point where I'm happy building in the hotend fan ducting.
Bad ducting can easily trip the heater fault mid print even with a silicone sock on the heater block. This occurs for me at temp set points between 210-230C running the stock thermistor and 30W heater cartridge.
Try to ensure the cross sectional area is most restrictive at the vent and increases back to the fan outlet. I think my current deign is too restrictive at the outlet of the fan.
Current iteration aims the vents to a point 7.5mm either side of the nozzle on the hotend.
Vents are currently 17mm*3mm either side, about half the CSA of the fan outlet.

Yes, a berd air style system would be nice, but I know I can get good results with a radial, up to the point where I need a heated enclosure.

DocTrucker

This isn't presentation of finished work! Never finished...

If the arrangement of the ducting is ok, the areas that I want to tackle next is to move the duct arms onto the bit that mounts the fan and industrial proxy sensor.

Following iteration will investigate feasibility of ditching the standard E3D fan mount and making a custom one so it gets a cleaner flow of air to the fan, and isn't impeding the design of the part cooling ducts as much.

zapta

@DocTrucker said in Part cooling fan duct (again!):

My Notes:

Anything about the smoothness of the inner surfaces? Printing hollow objects such as duct fan required very good part cooling.

I have a design that I am happy with and printed with PETG but am considering getting a smoother print from Shapeways.

A Former User

@DocTrucker said in Part cooling fan duct (again!):

Can you place your nozzle at 0.5 while cold

yes

turn part cooling to 100%, turn heater set point to 210C, and it get to temp without faulting out?

Yes.

I like to push all my heaters (hotend, hotbed..) overboard so have a bunch of hotends with 80-100W heater (and yes, seen some melted alu blocks in my days) so getting up to temp while blowing into the heater block is not a problem
I like to insulate my hotend from the environment so while back coated it with car gasket silicone (good up to 700C), was ugly and hard to repair, but worked superbly, these days I use those silicone socks (black one tend to be better than other colors, no clue why)
I also tend to use fan duct system that blows just below the nozzle, that just barely cool the nozzle and do not cool the heater block at all
I used to print them all in ABS and then smooth and strengthen them in acetone bath but I'm printing mostly PETG these days, it's not as smooth so the sound is bit louder than with smoothed ABS but my environment is so loud on it's own that I stopped caring, I just put my noise-canceling headphones and let the fans rip

If yes can you build the #3DBenchy with no rough patches on the bow?

with PLA, yes
with ABS, PETG - depends, with normal hotends I used to make - NO, with E3D steel - sometimes, with mosquito - no clue will let you know, with E3D X / mosquito+e3dX - no clue, will let you kno I have high hopes
with PC - no
with HIPS - yes
with nylon - no
with PP/HDPE - no

A Former User

@zapta said in Part cooling fan duct (again!):

Anything about the smoothness of the inner surfaces? Printing hollow objects such as duct fan required very good part cooling.

I did a lot of ABS and printed a lot of fun ducts, never found any difference in performance related to smoothness of the duct. main issue printing ducts is angles, if you have bad angles it will not print in ABS and with other materials it will print poorly. So proper design should print no matter what.. As for smoothness, you can really smooth the ABS with acetone, especially if you don't care about "small features" (like you don't on a fun duct as there are none) so you don't go nice with acetone vapor but you dump the whole part in acetone leave it there for tens of seconds get out (it will start to get soft), shake the acetone off it and let it dry for few days ... you get a solid piece of ABS (no layers exist after that, it's like injection molded) smooth as possible .. zero improvements in performance, air flow looks identical even on high speed camera, but sound levels drop significantly (I was getting lower sound levels with ducts then without ducts, just fan's alone on rubber stands)

DocTrucker

Thanks for the comments. Yes, I have been thinking about ditching the 30W cartridges for some time. I didn't have much issues when printing 180-200ish but as soon as it went over 200 it struggles on temp. That said wouldn't the PID tune just set the expected temp rise in 1sec to a larger number?

Regards smoothness I've not experimented with that and noise is a secondary concern to printed part quality. That said the layers are aligned to the airflow as it exits the nozzle.

A Former User

@DocTrucker said in Part cooling fan duct (again!):

ditching the 30W cartridges

While I overpower them, it's not required, for e.g. teartime is making printers that print their own brand of ABS that requires 270C for printing and they do it with 18W heater!!! I never had issue with TT printer heating abs to 270C and maintaining that temp.. (on the other hand their heaters can barely reach 100C so replacing bed heater is something one almost have to do)

DIY-O-Sphere

@DocTrucker said in Part cooling fan duct (again!):

That said wouldn't the PID tude just set the ecoected temp rise in 1sec to a larger number?

Just 2 ideas:
Have you checked the value of the safety temperature limit in config.g
Maybe it's set around 200°C
The other idea: pwm of the heater is limited in config.g

DocTrucker

@DIY-O-Sphere thanks for your comments. Couple of typos there now corrected!

My temp limit is set to 250 and there is no limit set on heater modulation. When it faults out it is a message saying sometjing along the lines of "Heater fault, temp rise of 0.9 degrees per second not met." I suspect this value is extrapolated from the PID tuning and if so, if I put a more powerful heater in its place I suspect this trigger value for the alarm will increase. Potentially meaning the trip still occurs, although as the cooling capacity of the fan system remains unchanged I guess the overall effect would be less.

DIY-O-Sphere

There is an instruction how to manually adjust the parameter.
I thing it's worth trying.

https://duet3d.dozuki.com/Wiki/Tuning_the_heater_temperature_control#Section_Manual_adjustments_to_the_heater_model_parameters

Or what about to repeat PID tuning with fan on?

wilriker

@DocTrucker did you do your PID tuning with the part cooling fan at 100%? That's at least how I learned to do it. This should take any effect the part cooling fan has on the temperature into account and thus mitigate your heater fault problems.

Also I had to redo my PID tuning a few weeks back with no hardware changes made to the system at all. Suddenly it was no longer able to even reach 100°C without faulting that it did not rise fast enough. Maybe you need to redo it also.

DocTrucker

@wilriker I did try that a while ago, but you've got me thinking perhaps there is an argument for two PID tunes. One for control and one for worst case heat up time fault detecton setup? The difference in the autotune results of fan off and fan on could also be a neat test to run from now on when changing the duct design.

DocTrucker

@DIY-O-Sphere I don't think you can tune the alarm point directly but will have anotherlook thanks. As above I have tried tuning with the fan on, I had an issue but can't remember what it was. Possibly excessive oscillation. Will try next week.

DocTrucker

@smece said in Part cooling fan duct (again!):

...zero improvements in performance, air flow looks identical even on high speed camera, but sound levels drop significantly...

How did you visualise flow?

DIY-O-Sphere

@DocTrucker
Just a question, do you use an external power supply connected to the boards 5V input?

DocTrucker

@DIY-O-Sphere yes. Think it's a 2A one.

DIY-O-Sphere

@DocTrucker
Are you also using a 5V part cooling fan?
Can you switch that power supply to an other one?
The reason is, I just remembered, that I had a similar problem in the past with my ramps.
The temp was freaking around the set point. And it was caused by a bad stabilised LM2596 DC step down module.
After adding a big capacitator to the 5V rail everything worked fine.

A Former User

@DocTrucker said in Part cooling fan duct (again!):

visualise flow?

the ones I was designing myself I was using some plugin for solidworks and later I was trying some plugins for onshape... not really very useful to me, neither of them, as I don't know 90% of the things they ask me to set before simulation + the printed part has so many imperfections + air source from the radial and axial fans makes a lot of difference and I have no clue how to set that up so.. it was interesting to play, useless for final design...

so I decided to go with the old proven way and use smoke and high speed camera ... high speed is on phones (I don't have real high speed camera, just bunch of samsung, google and apple phones that have that feature... lot of phones, my company makes apps so we have ton of phones for testing purposes, some have high speed capability ) and smoke I tried number of sources ... burning ABS smokes a lot, cigars (not cigarettes) have good thick smoke, vaping devices produce good smoke (it's I think vapor but who cares looks like smoke, visible..) etc etc .. but the best results I had with some heated oil for train models and smoke machine I lend from my brothers club... black background and good lighting ... now, last time I did it was over two years ago but I doubt any of my findings would be different these days.. and btw results from real life test vs simulators - 2 totally different things can't even compare

now the simplest test I seen ppl do (never tried myself) is with ball of water... it actually gives you air pressure info too so should be done when designing a duct (you put a ball of water under the hotend and look how the airflow disturbs the water surface - check example here 2:44 https://youtu.be/xmZCwJDyxYU?t=164 )

DocTrucker

@DIY-O-Sphere good to be aware of issues like that but no thanks, it's a 12VDC radial blower. The temp plot on tue web control looks smooth and noise free.

DocTrucker

@smece Cheers, thanks I was meaning how do you make it visible. I'd thought of the smoke bombs used to test gas fire exhausts but thought there was far too much smoke. Model train engine smoke generators is a great shout. Someone had mentioned the water trick before and I had completely forgotten!